The present disclosure relates to feed trays or stackers for holding sheet paper stock from which sheets are progressively fed into a copier or printer. Feeders for paper sheet stock may have the deck plate or bottom of the tray elevatable as sheets are withdrawn from the stack to maintain the top sheet of the stack properly positioned for correct entry when moved by a nudger into the feeder entry such as a pair of nip rollers. A common method to elevate stacks for feeders such as friction retard feeders containing one ream of paper stock, typically less than 600 sheets, is to elevate only the one edge of the stack of sheet paper stock nearest to the feeder nip thereby reducing the forces required to elevate the entire stack and minimize the complexity of the elevating mechanism. However, single edge elevation of the feeder deck plate inherently results in a sloped/angled approach of the stack into the feeder nip. Where heavy weight paper sheet stock is being fed, this has resulted in the leading edge of the top sheet contacting the roller above the nip centerline which results in sheet stubbing and the downward bending of the leading edge whereby the normal and friction forces developed between the bent top sheet and the next sheet beneath results in dragging the next sheet into the nip causing a misfeed.
In addition, as sheets are withdrawn from the stack, the elevation mechanism must raise the leading edge of the stack progressively higher resulting in a greater sloped angle of approach of the stack to the feed nip. The increased angle has resulted in the leading edge of the top sheet striking the upper nip roller even higher and further causing sheet damage and more frequent misfeeds.
Therefore, it has been desired to provide a paper sheet stock feeder which has a cost effective elevatable bed plate or tray which can accommodate the weight of a large stack of paper sheet stock and particularly heavy weight sheet stock and elevate the stack so as to maintain the top sheet for proper nudging into the nip of the feeder in a manner which is not complex, does not require an elevating force equal to the weight of the entire stack and which aligns the leading edge of the top sheet with the centerline of the feed nip at an very low angle of approach as sheets are withdrawn from the stack.
Referring to FIGS. 3 and 4, a known arrangement for a sheet paper stock feeder or loader is illustrated where the stack of sheet paper stock indicated generally at 1 has the top sheet thereof moved by a nudger roller 3 frictionally engaging the top sheet and rotated in a counterclockwise direction as indicated by the curved arrow for propelling the sheet 2 into a feeder nip indicated generally at 4. A sheet guide, denoted by reference numeral 5, lifts the leading edge of the sheet 2 from the stack to position the leading edge properly for entry into the centerline of the nip as illustrated in FIG. 3 for a full stack of paper in the tray or bed plate 6.
Referring to FIG. 4, the device of FIG. 3 is shown with the lead side of the bed plate 6 adjacent the leading edge 2a of the sheet 2 elevated by a crank arm 7 which is lifted by a distance “Y” and forming a tilt or slant angle for the bed plate 6 denoted by the character “a” in FIG. 4. Thus, the leading edge 2a engages the upper roller 8 of the feeder nip 4 at a distance “y” above the centerline of the nip which results in the top sheet 1 being deflected downwardly into the nip. This downward deflection causes increased pinching and friction between the top sheet and the next adjacent sheet in the stack and often dragging the next sheet into the feeder nip thereby causing a misfeed. This problem is particularly acute with heavy weight paper stock because the bending force of the top sheet 1 is increased by the greater stiffness of the heavier sheet stock thereby resulting in substantial downward friction force on the next adjacent sheet; and, thus there is a high probability of misfeed when the angle “a” is sufficient to cause the leading edge 2a to engage the upper nip roller 8 so as to cause significant bending of the top sheet 1.
Thus, it has been desired to provide a way or means of implementing a sheet paper stock feeder tray which may be elevated economically by a mechanism raising only one side thereof but which eliminates the occurrence of misfeed when the tilt or slant angle of the stack, resulting from withdrawal of many sheets, increases to a point where the leading edge contacts the upper nip roll above the nip centerline resulting in substantial downward bending of the leading edge of the top sheet.